Gut bacteria may be taking over our appetites and dictating how much we eat, research suggests.
The bugs decide when they have had enough nutrients and send chemical signals to the brain that cause us to feel full, say scientists.
The findings, from a study of rats and mice, highlight the close relationships animals including humans have with the microbes living in their digestive tracts.
Lead researcher Dr Serguei Fetissov, from Rouen University in France, said: "We now think bacteria physiologically participate in appetite regulation immediately after nutrient provision by multiplying and stimulating the release of satiety hormones from the gut.
“In addition, we believe gut microbiota produce proteins that can be present in the blood longer term and modulate pathways in the brain.”
The study, published in the journal Cell Metabolism, focused on Escherichia coli (E.coli) which normally live harmlessly in the guts of mammals and birds.
Although some strains of E.coli can cause food poisoning, the bugs usually benefit their hosts by keeping out other kinds of harmful bacteria.
Dr Fetissov’s team found that 20 minutes after consuming nutrients and multiplying, E.coli in the gut start producing different kinds of proteins.
It takes about the same amount of time for a person to start feeling full or tired after a meal — and this is no coincidence, the researchers discovered.
Analysis of the “full” proteins released by the bacteria showed that they stimulated the release of the YY peptide, a hormone associated with satiety.
They also boosted the firing of neurons in the brain that reduced appetite. The “hungry” proteins produced by the bugs before a meal did not have this effect.
“Our study shows that bacterial proteins from E.coli can be involved in the same molecular pathways that are used by the body to signal satiety, and now we need to know how an altered gut microbiome can affect this physiology,” said Dr Fetissov.
PA